This invention relates in general to a mandrel or form for making an elastomeric article by a dipping process and, in particular, to a one-piece mandrel formed of an elastically resilient material for making a thin-walled elastomeric article (such as a balloon). A particularly advantageous embodiment of the mandrel of the present invention, as described in detail below, is especially well-suited for making a balloon or like article having at least one opening or hole in the body thereof (i.e., a balloon or article having the shape of a torus or its topological equivalent).
A number of articles such as surgeons' gloves, translucent drug sundries, footwear, flexible squeeze toys, and metal-coated compounds are made by dipping processes. These processes include simple dipiing, where one or more coats are applied with no coagulate being used; the Anode process, where a form is first dipped into coagulate and then into an elastomeric compound (such as natural rubber latex); and the Teague process, where the form is first dipped into an elastomeric compound and then into the coagulate. Of these processes, the Anode process enjoys the most popularity.
In the case of latex articles formed by the Anode process, the form or mandrel, which is usually aluminum, porcelain or stainless steel, is first dipped into the coagulate and then into the latex compound which is contained in a dipping tank provided with mechanical agitation and a temperature controlled jacket. The form may be dipped manually or by automatic operation. After withdrawal, the form is usually rotated to ensure even distribution of the deposited latex. Leaching, drying and preliminary finishing operations such as beading or trimming then follow. The latex articles may be vulcanized in circulating hot air, steam or hot water. Vulcanization may take place on or off the form. The cured articles are then stripped from the form in a wet or dry condition. Finishing operations typically include washing and drying.
Due primarily to the nature of the stripping operation, it is inherently difficult to make relatively small, thin-walled latex articles, such as balloons, by a dipping process when such articles are provided with one or more openings in the bodies thereof. U.S. Pat. No. 2,053,372 to Lee relates to a technique for making irregularly shaped inflatable articles using forms which are collapsible so as to allow for their removal from the formed articles subsequent to the dipping process. FIG. 5 of Lee's patent shows a form 39 in the shape of a flying horse having a central opening 41 formed therein. Form 39 is made of a relatively rigid material, such as a filled manila paper, and is destroyed in the stripping process. According to Lee, it is not possible to make such a form of a flexible, collapsible material (such as rubber) since the form must be broken to remove the form from the article.
U.S. Pat. Nos. 1,841,886 and 1,948,608 show annular forms used in making relatively large endless tubes of rubber (i.e., inner tubes). Each of these forms is provided with a split to allow for removal of the formed tube, and a connecting element, such as a bolt or a locking mechanism, to draw the facing surfaces of the split together. While such an arrangement is appropriate for use in forming the relatively large, thick-walled articles described in these patents, a similar arrangement would be impractical to implement in manufacturing large numbers of relatively small, thin-walled articles (such as balloons) because, during the stripping process, too much time would be required to disconnect and reconnect the locking mechanism. Such an arrangement would also be impractical to implement in manufacturing relatively thin-walled articles because it would be difficult to obtain a substantially continuous surface in the vicinity of the split which is important in the manufacture of such articles without objectionable seams and flash.
An object of the present invention is to provide an improved form or mandrel for making elastomeric articles by a dipping process.
Another object of the present invention is to provide a mandrel which can be efficiently used in a high volume production setting to produce articles, such as balloons, which are provided with at least one opening in the bodies thereof.
Yet another object of the present invention is to provide a mandrel for forming articles having at least one opening in the bodies thereof in which the articles can be easily removed from the mandrel.
Still another object of the present invention is to provide a mandrel which has a substantially continuous surface permitting the manufacture of thin elastomeric articles without objectionable seams and flash.
A further object of the present invention is to provide a one-piece mandrel having a self-closing and self-aligning split through a cross-sectional portion thereof.
These and other objects of the invention are attained in a one-piece mandrel for making an elastomeric article by a dipping process, which has a one-piece body having at least one opening therein and a split extending from the opening through a cross-section of the body. The body is formed of an elastically resilient material so as to allow the split to be opened for removal of the elastomeric article after formation, and so as to cause the split to re-close after removal of the article from the mandrel to form a substantially continuous surface on the mandrel in the vicinity of the split. In a preferred embodiment of the invention, a portion of the one-piece mandrel body extends through a wall of the article. In an especially preferred embodiment, this portion provides a molding surface for forming a hollow stem on the article. The portion of the one-piece body which extends through the wall of the article is also preferably adapted for attaching the mandrel to a dipping apparatus.
In the preferred embodiment, the mandrel is provided with means for causing the mating facing surfaces of the split to self-align upon closure thereof. In one embodiment, the means for aligning the surfaces include the use of an "irregular" split in which at least one protrusion is formed on a first of the surfaces, and a mating depression is formed in the other surface. Alternatively, an alignment element, which is at least partially embedded in the one-piece body, may be used. A portion of the alignment element extends from a first of the mating surfaces, and a mating depression to accept the extending portion of the alignment element is formed in the other surface. In an especially preferred embodiment, the alignment element is formed of a ferro-magnetic material (such as steel), and a magnetized element is embedded in the mandrel adjacent the depression in the second of the mating surfaces to assist in holding the mating surfaces together during the dipping process.
In a preferred embodiment of the invention, the one-piece mandrel is formed of a silicon rubber compound having a Shore A hardness ranging from 20-90 (and preferably from 60-75), a tensile strength of 500-1,100 pounds per square inch, a percentage elongation of 150-360 percent, a tear strength of 55-120 pounds per square inch, and a continuous service temperature rating of at least 212.degree. F. Such material is resistant to water, mild acids and bases.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.